Author Topic: Measuring Foil Angles  (Read 2731 times)

Admin

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Measuring Foil Angles
« on: December 25, 2020, 09:14:46 AM »
Hi guys,

Here is a nice way to measure some interesting elements of your foils that aren't commonly listed by manufacturers. 

It uses only a mm ruler, is highly accurate, it can be duplicated and it should provide a nice way of sharing info.

The Axis foils have a nice feature where the fuselage is level when resting on the area where the mast inserts.  You can check this with a digital level.  So, if you rest that area on a level surface (check that as well), you can individually measure the incidence (the angle difference from a single foil to the fuselage) of the stabilizer and of the front wing. 

To do that you can measure up from your level surface to both the leading edge and the trailing edge of the wing.  The difference between those two measurements will be your rise.  Height A minus height B = Rise.

To get run you can just measure the chord of that wing.  Rise over Run = Slope but degrees are nicer and here is an easy calculator:  https://www.inchcalculator.com/rise-run-degrees-calculator/

Once you have the positive angle for the front wing and the negative angle for the rear wing you can also get the angle difference if desired.  Front Angle - Back Angle. 

As an example my Axis 980 with the 420 tail is .54 front incidence minus - 1.91 rear incidence =  2.45 angle difference.

There are a few details that need to be minded such as a level "lifter" for the fuselage but those are easy to accommodate with household items.


« Last Edit: December 25, 2020, 09:46:59 AM by Admin »

Admin

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Re: Measuring Foil Angles
« Reply #1 on: December 25, 2020, 09:16:48 AM »
Here is an example of a tail wing incidence measurement:
« Last Edit: December 25, 2020, 09:29:17 AM by Admin »

PonoBill

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Re: Measuring Foil Angles
« Reply #2 on: December 25, 2020, 09:50:45 AM »
Or you can get one of these:



eFlite anglepro II
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Admin

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Re: Measuring Foil Angles
« Reply #3 on: December 26, 2020, 01:55:05 AM »
This is nice because it is free, very accurate, quick and easy.  Could be great for sharing info. 

When you look at the images above and zoom in you see why many of the existing angle tools that are sometimes used are too coarse.  Even the trailing edge on a stabilizer is a mm.  This easy measurement will get duplicable accuracy at home with free household tools.  I like that a lot.   

Thatspec

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Re: Measuring Foil Angles
« Reply #4 on: December 26, 2020, 02:28:29 AM »
Thanks Admin, I am going to try this in the near future with the new Gong stuff I haven't been able to even try yet. At least I can spend some quality time with it  ;D

Admin

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Re: Measuring Foil Angles
« Reply #5 on: December 26, 2020, 03:24:05 AM »
Sweet, I am interested to see what they are doing there.  Please post up what you find.

Right now I am freezing my ass off.  A drunk driver took out the gas for Hood River, White Salmon etc. since Tuesday and now that they turned it to full off, even our heat pump (electric) won't work due to a system safety thing that I can't override.  Arggghhhh!

clay

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Re: Measuring Foil Angles
« Reply #6 on: December 26, 2020, 08:15:01 AM »
Thanks for sharing another way to measure this.  Stab angle can be such a game changer and knowing where one is at is super helpful.

I looked into a trying to find something off the shelf and didn't find anything.  I ended up making something out of wood like the eflite that straddles the fuse and then put a digital angle meter on it.  Now I know how much each hotel key card shim changes the angle.
Aloha, I welcome and appreciate all responses of positivity and good feeling.

YouTube: https://www.youtube.com/channel/UCOIE6FWr1SpWvbPJIIiEgog

PonoBill

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Re: Measuring Foil Angles
« Reply #7 on: December 26, 2020, 09:37:47 AM »
It's a useful approach for newer Axis systems, but not many other designs that either build the fuselage into the mast (GoFoil, etc,) have a projection that prevents the fuselage from laying flat (older Axis, etc,) or have a fuselage too thin to keep the wing from holding it off the measuring surface. You can work around all those issues with some ingenuity, but it's not automatic.

The first approach I used--notching the jaw of vernier calipers and placing an accelerometer-based angle meter on it is accurate and cheap, especially if you already have a drawer full of calipers and another of angle meters, but most inexpensive digital calipers have a 6 inch range, and ones with larger range are relatively expensive and rare. I have probably five 6-inch calipers ranging from ancient vernier calipers, to dial calipers to modern digital ones (people still call them vernier calipers despite the fact that dial and digital ones do not use vernier scales) collected over 50 years of wrenching, but none longer. I couldn't measure any low aspect wings. So I spent the 60 bucks.

The thickness of the trailing edges is inconsequential if the gauge is consistent. A V-notch places the measurement point at the center of the edge. Making a ruler measurement requires the same kind of consistency but it's not automatic. Choose the top or bottom to make the measurement or measure both and average to get the center (maybe). For the much thicker, curved leading edge that's a bigger problem. The V-notch consistently (if not accurately) measures the center of the curves. Measuring to the contact point of the leading edge just measures the tangent of the curve at that point. Unless the radius of the curve is consistent top to bottom or the foil is symmetrical that is not the center. I haven't seen any hydrofoils like that. 

Direct measurement of the relative angle of stabilizer to wing is quick, easy, direct, and consistent with a tool designed to make that measurement since you can set the gauge to zero for the wing and then measure relative stabilizer angle regardless of how level the board, mast plate, mast, and fuselage are.

For anyone convinced that these angles affect performance (which by now should be about anyone) buying a 60 buck tool to help your minimum $3K investment work well doesn't seem out of the question. It seems more likely that anyone interested in measuring this factor would take the minute or two required to use the tool rather than spend a lot of time figuring out how to make using a ruler work with their flavor of foil.   

I'm still struggling to understand your notion that the angle of each lifting surface relative to the fuselage is more important than their angle relative to each other.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

PonoBill

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Re: Measuring Foil Angles
« Reply #8 on: December 26, 2020, 11:09:28 AM »
Sweet, I am interested to see what they are doing there.  Please post up what you find.

Right now I am freezing my ass off.  A drunk driver took out the gas for Hood River, White Salmon etc. since Tuesday and now that they turned it to full off, even our heat pump (electric) won't work due to a system safety thing that I can't override.  Arggghhhh!

Get in touch with Tad. As I recall you guys have used his handyman service before. He's managed to contact the supervisor of the crews working to restore service. He can probably help you get back quicker. If nothing else there are a couple of electric heaters at my shop. Tad can get them for you.

I consider Tad to be the most important person to know in Hood river. 
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

PonoBill

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Re: Measuring Foil Angles
« Reply #9 on: December 26, 2020, 11:12:55 AM »
Incidentally, using your measurement system the surface doesn't need to be level as long as it isn't angled enough so the wing slides off--it just needs to be flat.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Admin

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Re: Measuring Foil Angles
« Reply #10 on: December 26, 2020, 12:25:15 PM »
Now I know how much each hotel key card shim changes the angle.

It sounds like you have a great system.  There are a number of uses but what you mentioned is likely the most common.  With Axis we are adjusting the stabilizer only.  It is great to get a start angle, add a shim (possibly a washer) and quickly check what you have done.  Checking stabilizer incidence is a matter of seconds.   For that you can just rest the fuselage itself on a known flat surface and take the 3 measurements.  Less than a minute all in.  I like to put a little weight right above the mast hole on the fuselage so everything is held rock solid.  Movement can soil any of these systems.

Getting all of the 3 measurements was really interesting to me with the new Axis Black stuff.  I wanted to see what Axis had done.  The front wing incidence on the 980 on the Black fuselage is .54 degrees where it is 2.58 degrees on my 860 on the red fuselage.  The same 390 tail is -2.15 degrees on the black and 2.51 on the red.  Interesting that in lowering these angles, Axis lowered the front incidence much more significantly than the rear.  Looking at this stuff on a granular level is great.  We are all students of these interactions and it is nice to have an easy system to break it down.


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Re: Measuring Foil Angles
« Reply #11 on: December 29, 2020, 02:35:47 AM »
Here is a graphic for the Axis foils that I have here.  It helps me think about the relationships to visualize it with the board as well.  This shows a few incidence variations on  both the Red fuselage and the Black fuselage using the numbers (evened out for simplicity) from the foils I measured above.  It shows the native setting for each with no shims and then 2 variations for each fuse.

Most interestingly to me it shows what the adjustment would look like to match the native angles of the other fuse. 


« Last Edit: December 29, 2020, 08:03:40 AM by Admin »

Dwight (DW)

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Re: Measuring Foil Angles
« Reply #12 on: December 29, 2020, 03:33:24 AM »
on the top image (black) shouldn’t it be labeled with supplied shim.

Middle image labeled with stock shim removed.

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Re: Measuring Foil Angles
« Reply #13 on: December 29, 2020, 03:45:12 AM »
Hey Dwight, I didn't do one with the included 1 degree down-shim because I haven't been using it.  I took my measurements with no shim.  By native I mean no shim at all.  The second example for the black fuse would have an up-shimmed tail and the third would have a significantly down-shimmed tail (that one is a more extreme version of what your down-shimmed 980/420 setup would look like with the included shim). 

My Axis 980 with the 420 tail is .54 front incidence minus - 1.91 rear incidence =  2.45 angle difference.  I am assuming that the intention was probably -2.0 degrees incidence in the rear with no shim.  It would be -3 degrees with the provided shim for a total angle difference of 3.5 degrees (again cleaning up the numbers a bit).
« Last Edit: December 29, 2020, 04:00:24 AM by Admin »

Dwight (DW)

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Re: Measuring Foil Angles
« Reply #14 on: December 29, 2020, 04:23:02 AM »
I was under the impression the shim on the black puts the stab angle at the red level. So by this diagram with shim, black has more Stab angle than red. It’s not making sense to me.
« Last Edit: December 29, 2020, 04:43:18 AM by Dwight (DW) »

 


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